Grapes are customarily harvested at a sugar level of about 16 percent Brix. This value can be determined by randomly selecting one or more berries from a bunch of grapes to be marketed, squeezing out the juice, filtering if necessary to remove solids, and "reading" the juice with a hand refractometer to determine the % Brix. This method is described generally in the publication by the California Department of Food and Agriculture entitled "Fruit and Vegetable Standardization," Title III, Article 25, sec. 1436.5 (Register 75, No. 4, 1-25-75). For purposes of the present application an additional method has been employed to determine the sugar level. This method (designated as the "Sugar Content") involves selecting the second bunch on each cane (most vines have four canes), selecting the second shoulder in the bunch, removing all grapes, admixing and extracting the juice from all of these berries followed by reading the % Brix as above. The values from the four canes are then averaged to give the "Sugar Content" for the grapes on a particular vine. Another parameter measured for purposes of the present invention is the acid level of the grapes. This value is determined by titrating the juice used in determining Sugar Content against NaOH. This method is described in the California Department of Food and Agriculture publication described above, Article 25, section 1436.7 entitled "Grapes, Titration to Determine Soluble Solids to Acid Ratio." The sugar/acid ratio used in the Example is determined by dividing the Sugar Content by the acid value.
In California and other areas, it is customary to harvest grapes when the % Brix reaches 16 percent. In many situations it is desirable to hasten the increase in sugar level to the desired 16 percent level or higher (for wine grapes, raisins) so that the orderly harvest, processing and marketing of the grapes (or products therefrom) can be maintained. Accordingly, a major objective of the present invention is to enable grapes to be harvested "on schedule".
The use of ammonium isobutyrate (AIB) as a ripening agent for sugarcane is described in U.S. Pat. No. 4,033,755. Other relevant U.S. Pat. Nos. included 3,870,503 (sodium isobutyrate), 3,909,238 (polyethoxylated surfactants), and 3,994,715 (vanillin).